This invention relates to security systems and, more particularly, to a novel and highly-effective security system which reliably gives an alarm when unauthorized persons gain access to a protected space by opening a door or window, etc., but which permits access to the protected space by authorized persons without giving an alarm.
Security systems which will give an alarm upon unauthorized entry into a protected space but which will permit authorized entry into the protected space without giving an alarm are known. Typically, however, persons making authorized entry into the protected space must take some obvious action in order to silence the alarm, such as throwing a wall-mounted switch or using a special key. Such a system suffers from the disadvantage, among others, that its existence is in effect advertised for all to see. This may put burglars or others intent upon unauthorized entry on notice that the space in question is protected by an alarm system and that countermeasures will be necessary. The burglar or other intruder makes a systematic search for the contacts that become separated when the door or window, etc., is opened and, in some cases, is able to circumvent the system by the simple expedient of placing a shunt around these contacts.